The instant invention relates to a process for piecing back to a spinning device operating with a pneumatic torsion element in which a yarn which is fed back to a drafting mechanism is brought together with a roving, as well as to a device to carry out the process.
In a known process of this type the pair of intake rolls of the drafting mechanism is stopped for the purpose of piecing back when a yarn breakage occurs, so that the roving or the fiber sliver is opened in the drafting zone which follows this pair of intake rolls (DE-OS 3,411,577 and 3,413,894 corresponding with U.S. Pat. Nos. 4,550,560 and 4,545,193, respectively). When the fiber sliver or the roving is fed back to the torsion element for piecing, an irregularity is produced which must be removed from the finished yarn in a further step.
It is therefore the objective of the instant invention to create a process and a device which makes it possible to produce an unobtrusive piecing joint with little expenditure.
This objective is achieved according to the invention in that the roving, after being stopped, is at first released for the piecing process and in that the forward end of the roving which is leaving the drafting mechanism is sucked away until the roving segment which has remained in the drafting mechanism during the prior stoppage of the roving has been taken away, and in that the roving is subsequently fed to the torsion element while being simultaneously brought together and combined with the yarn end. Due to the stoppage of the roving or of the fiber sliver said roving or said fiber sliver is not only discontinued, but its forward end is given an irregular shape which is unsuitable for piecing. Therefore the removal of this affected forward end of the roving or sliver ensures that in piecing a segment with unaffected fiber orientation and length is fed to the torsion element to be combined with the yarn. In this way, even and unobtrusive piecing joints are obtained.
In the sense of the instant invention, roving is understood to be any sliver-like material which can be fed to the torsion element by means of a drafting mechanism, regardless of whether it has little torsion or not. Not only flyer rovings but also card slivers etc. fall therefore into this category.
In order to coordinate the re-starting of yarn torsion in a particularly simple manner with the beginning of yarn draw-off, whereby the length of the piecing joint can be predetermined precisely, it is preferable to draw off the yarn at first through the torsion element without it exerting any twisting action upon the yarn, whereby furthermore, in function of the position of the end of the yarn previously fed-back, the removal of the roving is ended and the feeding of the roving to the torsion element is started, roving and yarn now being submitted together to the twisting effect which now begins.
It is basically sufficient if the yarn and the stretched roving are allowed to run together into the twisting nozzle. However, the longer the common conveying path of roving and yarn between drafting mechanism and torsion element, the better the piecing joint. For this reason provisions can be made in a preferred embodiment of the inventive process for the yarn to be introduced laterally into the closed clamping line of the two output rolls and to be fed necessarily to the torsion element at the speed determined by the rotational speed of the two output rolls.
To prevent the injector effect in the torsion element from provoking uncontrolled draw-off of the yarn after the feeding of compressed air is resumed provisions are made in a preferred version of the process for the yarn which is brought together with the roving to be retained pneumatically and to be furthermore braked mechanically upon resumption of yarn draw-off until part of it is brought together with the roving. The yarn is thus drawn off at a draw-off speed which is dictated mechanically by the winding device or by a pair of draw-off rolls. Beyond this, the yarn in the process of draw-off is controlled between yarn holding device and torsion element until further controlled yarn draw-off is ensured by bringing together the yarn and the roving. Perfect and unobtrusive piecing joints are ensured in this way.
The success of the piecing process does not only depend upon the state of the forward end of the roving but also upon the state of the yarn end. For this reason it is advisable for the end of the yarn which is to be brought together with the roving to be subjected to a pre-treatment before this joining together. This is done preferably by measuring out the yarn to a defined length. The position of the yarn end in the process of being drawn off and which is thus brought to a determined length can then be sensed and can be used as a basis to control further phases of operations in the piecing process, for example in starting roving feeding, in controlling roving suction, in controlling compressed air feeding to the torsion element, etc.
To carry out the process the invention provides for the mouth of a suction nozzle to be brought into action alongside the conveying path of the fiber material between the two outlet rolls of the drafting mechanism and the torsion element. Before piecing the roving is not conveyed through the drafting mechanism but is stopped by the roving stopping device. Depending upon the configuration of the roving stopping device (for example a stoppable pair of intake rolls of the drafting mechanism or a roving clamping device) the forward end of the roving is given a form which makes it impossible to obtain an unobtrusive piecing joint, so that said joint must be removed in a subsequent cleaning process. In order to avoid this, the instant invention provides, after release of the roving, for the affected forward end of the roving to be taken away by means of the suction nozzle mouth which can be activated alongside the conveying path of the fiber material, so that a faultless segment of roving then becomes available for piecing.
To be able to precisely synchronize the moment at which the spinning overpressure in the torsion element is switched on with the moment when yarn draw-off begins and when the negative pressure at the suction nozzle is switched off, the suction nozzle and the torsion element can be connected via a control device to a yarn-end supervision device which is attributed to the pneumatic yarn holding device for this switching off of the negative pressure at the suction nozzle and switching on the overpressure at the torsion element. In this way, a defined transfer of the forward end of the roving from the suction nozzle to the torsion element is achieved, and this is essential for the obtention of good piecing joints.
To exclude uncontrolled yarn movement and uncontrolled start-up thereof through the pneumatic torsion element when the yarn running into the torsion element is being held in a pneumatic yarn holding device, and thereby to avoid irregular piecing joints, this pneumatic yarn holding device is advantageously associated with a yarn brake which acts upon the yarn in the process of draw-off.
In order for the yarn to be fed back without interference, the yarn brake is preferably controllable by means of a controlling device and can be brought by said controlling device into or out of the path of the yarn extending into the yarn holding device. It is advantageous here, in order to ensure faultless guidance of the yarn with respect to the yarn brake, if said yarn brake is located in the yarn holding device which is fashioned as a suction pipe.
However, the quality of the piecing joints is not only influenced by the shape of the forward end of the roving but also by the shape of the yarn end. To ensure that not only a forward end of the roving of perfect quality but also a defined yarn end is available for piecing, a pre-treatment device which can be used on the yarn is suitably provided in a further embodiment of the object of the invention. This pre-treatment device is preferably made in the form of a yarn separating device and is installed in the yarn holding device which is made in form of a suction pipe.
It is customary to carry out piecing with the help of a piecing carriage which can travel alongside the machine and which can be brought to any spinning station at will. In this case the controlling device for piecing is advantageously installed on the piecing carriage, especially the suction nozzle, the yarn holding device as well as a controlling device which can be brought to bear upon the roving stopping device.
To avoid that the pneumatic yarn holding device cover long distances or any distance at all during feed-back of the yarn, the torsion element can, in addition to a first set of compressed air bores with a direction component in the direction of yarn draw-off and which are subjected to compressed air during normal spinning operation, be furthermore associated with a second set of compressed air bores with a direction component in feed-back direction and which are subjected to compressed air during the feed-back of the yarn into piecing position. The torsion element is preferably associated with a first stop which determines the spinning position of the torsion element and which is provided with a first compressed air feeding opening that can be connected to the first set of compressed air openings, as well as with a second stop which determines the threading position and which is provided with a second compressed air feeding opening which can be connected to the second set of compressed air openings.
Preferably each of the two compressed air feeding openings can be provided with a check valve which can be opened by application of the torsion element to the corresponding stop. The second stop is suitably installed on a piecing carriage which can travel alongside the machine and can be brought to any spinning station at will.
To suck away the fly which is produced in continuous spinning operation and to take away a ruptured yarn segment, a preferred embodiment of the object of invention is equipped with a suction nozzle after the torsion element (as seen in spinning direction) near said torsion element and directly next to the yarn conveying path.
The invention ensures reliable piecing and unobtrusive piecing joints with a device of simple design. Only orderly material is presented for piecing, so that no danger exists for the torsion element to become clogged because of non-oriented fibers and consequently for yarn breakage to be provoked.